Both lung and kidney microsomes possess the necessary enzymes to convert bromobenzene to p-bromophenol and p-bromophenol to bromocatechol and to convalently bound material. Moreover, a portion of the extrahepatic covalent binding derived from bromobenzene can be attributed to reactive metabolites of p-bromophenol which presumably are formed from the oxidation of bromocatechol to the quinone. The role of these reactive bromophenol metabolites in bromobenzene induced toxicity is nuclear.